This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present system and techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The present embodiments generally relate to grounding assemblies, and, more particularly, to grounding assemblies for motor shafts, turbine shafts and other rotating shafts conductively linked to components that create an electrical charge, or that may experience a build-up of electrical charge.
Electric motors often experience induced electrical currents in shafts. More particularly, motors employing variable speed drives that utilize pulse width modulation technology to vary the speed of motors have an increased susceptibility to such currents. For example, using motors with variable speed drives includes the caveat of a higher common mode voltage (CMV) generated by the variable speed drive, which increases shaft induced currents.
Voltage on the motor shaft induces current flow through the shaft bearings to the motor frame and then to ground. During motor operation, charge may build up on the shaft surfaces. In some instances, electrical discharge may occur, which causes electric discharge machining (EDM). EDM can damage the surfaces of shaft bearings and the balls in the bearings. The electrical discharge may create fusion craters, and particulate from the crater formation may remain inside the sealed bearing. Both the fusion crater and the particulate material in the bearing act to disturb the free flow rotation of the bearing, which can lead to physical damage and premature failure of various motor components.
The accumulated liquid can interfere with the operation and performance of the grounding assembly. In certain situations, various contaminants can migrate to the current control portion of the assembly. These contaminants may not allow proper performance of the assembly, causing which can result in damage to the shaft, bearings, or motor, resulting in deteriorated performance. Furthermore, removal of the assembly for periodic cleaning is time-consuming and may not be practical for substantially continuously operating equipment.